Field of the Invention
The present invention relates to a power take-off (hereinafter referred to as “PTO”) unit for a four-wheel drive vehicle, more specifically, a PTO unit that takes-off power from a transmission driving either front or rear wheels and outputs the taken-off power to the other front or rear wheels.
Related Art
A utility vehicle as disclosed by JP 2008-95711 A serves as a conventional four-wheel drive vehicle. This four-wheel drive vehicle is equipped with a prime mover, e.g., an engine, a first transaxle for driving either front or rear wheels, and a second transaxle for driving the other front or rear wheels. The first transaxle includes a transaxle casing incorporating a transmission, e.g., a gear transmission, for transmitting power from the prime mover to the corresponding front or rear wheels, and a PTO unit is mounted on the transaxle casing of the first transaxle so as to take-off power from the transmission of the first transaxle and so as to output the taken-off power to the second transaxle.
In this regard, the first transaxle includes an input shaft of the transmission projecting outward from one right or left side portion of the transaxle casing of the first transaxle, and another transmission, e.g., a belt transmission, is provided on this right or left side portion of the transaxle casing so as to transmit power from the prime mover to the input shaft. The PTO unit is mounted on the other right or left side portion of the transaxle casing opposite the input shaft in the lateral direction of the vehicle because the PTO unit can be designed to orient its PTO shaft in various directions freely from the input shaft and the other transmission on the opposite side of the first transaxle.
The transaxle casing of the first transaxle supports right and left differential yoke shafts drivingly connected to the corresponding wheels and provided with respective disc brakes. Each disc brake includes fixed discs fixed to the transaxle casing and rotatable discs rotatably integrated with the corresponding differential yoke shaft. These disc brakes are operatively connected to a brake pedal equipped on the vehicle so as to serve as foot brakes.
The capacities of the foot brakes have to be limited because increasing the capacities of the foot brakes means expansion of the discs against the desired minimizing and lightening of the vehicle. However, such limited capacities of the foot brakes may cause insufficient braking forces of the foot brakes for surely keeping the vehicle braked or parked on a slope from unexpectedly descending the slope, especially when the vehicle is heavily loaded or is on a steep slope.
To supplement the braking force, one conceivable solution is to additionally provide a parking brake on the vehicle. Disc brakes or drum brakes provided in rims of the wheels or on hubs of the wheels serve as typical parking brakes. However, such brakes have parts exposed to the outside of the vehicle, so that the exposed parts are likely to be wetted or covered by water or mud so as to impair the braking performance of the parking brakes.